In 1990, Congress specified that fuel with 10 percent ethanol (E10 or regular) could be sold year-round to encourage use of ethanol blended fuels, which provide significant reductions in tailpipe emissions. This Reid Vapor Pressure (RVP) waiver for E10, however, predated the introduction of higher ethanol blends like E15, which have an even lower RVP. Despite having lower emissions than E10, low cost, low carbon E15 cannot be sold in the majority of states during the summer months, except temporarily through emergency waivers.